fix(GroupAccount): Implement clear() method to correctly flush/empty group's content (refs #4539)
test(GroupAccount): Add test for GroupAccount::Clear() (refs #4539)
test(Dir): Add test for Dir::Clear() (refs #4539)
Merge pull request #1100 from eguaj/3.2-A4539

fix(GroupAccount): Implement clear() method to correctly flush/empty group's content (closes #4539)